This invention relates to compositions having a thickened fluid form, to a process for their production and to their use. In particular, the invention relates to compositions comprising a phase formed from a particular type of gel which may be used, for example, as hair treatment compositions and personal wash compositions.
Suspending agents are commonly employed in a variety of different types of compositions (eg, in hair treatment compositions) in order to improve stability against separation of the components, especially settling of suspended materials.
Examples of suspending agents commonly used in hair treatment compositions include crystalline suspending agents (such as ethylene glycol distearate) and inorganic structurants (such as swelling clays). Although these materials are effective for suspending particulate matter, they can adversely affect lathering performance and impart an undesirable cloudy appearance to the composition. Furthermore, during use of the composition they tend to get co-deposited along with the ingredients it is desired to deposit, which can lead to dulling of the hair through excessive build up and reduced performance.
The prior art also proposes the use for suspending purposes of hydrophilic polymers which disperse in aqueous media. Natural polymers have been used for this purpose, and in particular xanthan gum has been used. Personal washing products, especially shampoos, containing xanthan gum are described for example in U.S. Pat. No. 5,286,405 and GB-A-2188060. A problem is that the resulting products often have an unacceptable xe2x80x9cstringyxe2x80x9d texture and a slimy feel.
One category of synthetic polymers used for suspending purposes are carboxyvinyl polymers. The carboxyvinyl polymers are colloidally water soluble polymers of acrylic acid cross-linked with polyallylsucrose or polyallylpentaerythritol, obtainable under the CARBOPOL trademark from B F Goodrich. U.S. Pat. No. 5,635,171 describes a transparent or translucid gel based on such polymers, in which the gel is rigidified by the incorporation of a very small quantity of an aqueous solution of galactomannan (carob, guar or tara gum). This rigidification enables the stabilization of suspended phases.
A problem is, however, that carboxyvinyl polymers of the above described type can be difficult to formulate because of, inter alia, their sensitivity to pH and ionic strength and their incompatibility with ethoxylated surfactants.
A number of polymers of biological origin, when in aqueous solution, have the ability to form so-called reversible gels, for example, those which melt when heated but revert to a gel when cooled down subsequently. One well known example of a polysaccharide which forms reversible gels is agar. An aqueous solution containing a small percentage of agar is a mobile liquid when hot, but when left to cool it forms a gel with sufficient rigidity to maintain its own shape. Other naturally derived polymers which can form reversible gels are carrageenan, furcelleran, gellan and pectin.
The formation of gels by natural polysaccharides arises from interaction between the polymer molecules. Reversible gels generally melt over a range of temperatures or display a melting temperature, referred to as the gel point. This is the temperature at which, on slow heating, the gel is observed to melt as this interaction largely disappears. Thus, above the gel point, the hot solution of polymer is mobile. When it cools below its gel point, the interaction of polymer molecules enables them to form a continuous and branched network which extends throughout the sample. In contrast with the formation of a continuous, branched network, some other materials which thicken water do so through merely local, transient entanglement of molecules. A discussion of polysaccharide gels, including their range of mechanical properties, is found in xe2x80x9cGels and Gellingxe2x80x9d by Allan H Clark which is Chapter 5 in Physical Chemistry of Foods, Schwartzberg and Hartel, editors; published by Marcel Dekker 1992. In some instances, there is hysteresis and the melting and setting temperatures are not identical.
The melting temperature of a gel can suitably be measured by placing a steel ball, having a diameter of approximately 1 mm, on the surface of a sample which is fully set, then raising the temperature slowly, e.g., in a programmable water bath. The gel melting point is the temperature at which the ball begins to sink through the sample. Apparatus to facilitate such determinations is available, for example as a Physica AMV200 rolling ball viscometer from Anton Paar KG.
A reversible gel also displays a transition temperature at which, upon slow temperature increase, all ordering, be it of microscopical or macroscopical extent, has disappeared completely. This transition temperature (from order to disorder) can be measured by means of differential scanning calorimetry (DSC). The transition temperature of a reversible gel, as measured by DSC, usually approximately coincides with gel melting, observable visually.
EP-A-355908 teaches that polysaccharides which are capable of forming a reversible gel can be used to form viscous, yet mobile, fluid compositions by subjecting the composition to shear while gel formation takes place. The resulting compositions can be termed xe2x80x9cshear gelsxe2x80x9d.
Another way of forming a shear gel is to use a protein gel rather than a polysaccharide gel. An example of this is using a cold set whey gel as disclosed in U.S. Pat. No. 5,217,741, which is a gel created from pre-formed whey aggregates when the pH is changed or salt is added. This cold set whey gel can be produced as a shear gel of similar properties to that of the polysaccharide shear gels.
EP0250623 discloses the formation of whey particles by heating the whey solution under high shear to produce small heat set particles, that can be used as a fat replacement. The particles are not described as entrapping any material, nor are they described as a fluid gel with apparent yield stress properties.
We have now found that compositions comprising a continuous phase formed from such shear gels not only display excellent resistance to separation of components and settling of suspended materials but also can be used to entrap beneficial materials within the gel particles. xe2x80x9cEntrapxe2x80x9d is a used to describe situations where the beneficial materials are residing within a single gel particle and/or where the beneficial materials are associated with the gel matrix structure. The shear gels of these compositions are tolerant to the presence of many surfactants (eg, in personal wash or hair treatment compositions), and may under some circumstances enhance the delivery of the beneficial materials from the compositions.
WO98/08601 describes aqueous compositions such as liquid personal cleansers containing large hydrogel particles formed by two different water soluble polymers. The hydrogel particles trap water insoluble benefit agents in a network formed by these two polymers. The system is not a shear gel since it is prepared by first forming elongated polymer gel noodles which after gel formation are subsequently cut/broken into the desired gel particle size. The second polymer (which is typically an acrylic polymer such as CARBOPOL(trademark) referred to above) is required to modify gel strength in order to help stabilise benefit agent in the polymer hydrogel system. WO95/12988 refers to suspensions or dispersions of gelled and hydrated biopolymer particles for use in food or personal care products to impart a fatty-like character to the product. This system is not a shear gel since particulation of dry material at a temperature equal to or above T(gel) is followed by hydration of the particles at a temperature lower than T(gel), the term xe2x80x9cT(gel)xe2x80x9d denoting the temperature at which, upon cooling, an aqueous solution of the biopolymer concerned, sets to a gel.
WO99/51193 discloses hair treatment compositions comprising a first (shear gel) phase and a second (suspended) phase. The second (suspended) phase is suspended in the shear gel phase ie, between the gel particles in any fluid that is present between the particles. Thus, in this document, the compositions are produced by forming the shear gel as a first step and then adding the material of the second (suspended) phase as a second step. It is clear that under these conditions the material of the second (suspended) phase may become associated with the exterior surface of the gel particles but that the gel particles will not substantially encapsulate the material of the second (suspended) phase.
WO99/26585 describes a washing composition containing an emulsion of silicone droplets. The silicone droplets contain a dispersed phase of solid particulate active agent, such as, for example, zinc pyridinethione (ZPTO). The silicone phase is a liquid phase, rather than a gel phase.
EP-A-0630580 teaches oil-coated gellan microparticles for use in foodstuffs as fat replacers. The microparticles may be used to encapsulate drugs, micro-organisms or enzymes. However, there is no disclosure in this document as to how such encapsulating microparticles may be formed, other than by way of extending a fluid gellable composition containing the material to be encapsulated through a hollow needle or fine orifice. The resulting product is not a shear gel.
WO98/11877 describes the formation of a dry powder produced by spray-drying gel-encapsulated liposomes. The product of the process is not discrete microencapsulated particles but a homogenous mass.
WO98/5000 relates to crushable gel beads formed of an agar complex as delivery vehicles for the topical delivery of biologically or cosmetically active agents.
EP-A-0590538 describes hair treatment compositions in which hair treatment compounds are encased in a shell material.
U.S. Pat. No. 5,089,269 teaches a cosmetic composition comprising micro-capsules enclosing a hydrophobic component. The micro-capsules are composed of a gelatin film swollen with water.
U.S. Pat. No. 5,641,480 discloses hair care compositions containing heteroatom-containing alkyl aldonamide compounds and hair conditioning agents.
The present invention provides shear gel compositions which comprise a phase that is entrapped in the gel particles.
The entrapment of active substances in the gel particles may cause the substances to have enhanced delivery to the site of action eg, controlled release and/or more selective delivery. Also, the entrapped phase has a reduced tendency to separate from the composition.
In a first aspect, the present invention provides a composition which has a thickened fluid form comprising:
(i) a first (shear gel) phase comprising at least one polymer which is capable of forming a gel, which polymer is present in the composition as a shear gel (i.e., a multiplicity of separate gel particles which have been formed by subjecting the polymer to shear while gel formation takes place); and
(ii) a second (entrapped) phase which is in the form of particles or droplets comprising a hair benefit agent wherein at least some of the particles or droplets are entrapped in at least a proportion of the gel particles of the first (shear gel) phase.
In a second aspect, the invention provides a process for producing the composition of the invention which comprises forming an aqueous solution of the polymer, mixing the solution with particles or droplets of one or more hair benefit agents, which are substantially insoluble in the aqueous solution or substantially immiscible with the aqueous solution, and cooling the solution to a temperature below the gel formation temperature while applying shear to the composition.
In a third aspect, the invention provides the use of gel particles in a shear gel as a matrix for the controlled release and/or delivery of a substance which is entrapped in the matrix, in a hair treatment composition.
First (Shear Gel) Phase
In the present specification, the expression xe2x80x9cthickened fluidxe2x80x9d is used to denote a composition with viscosity greater than that of water.
In order that the gel particles remain stable in the presence of surfactant (which will normally be present in hair treatment compositions of the invention), it will generally be desirable that the polymer does not require polyvalent cations in order to form the precursor molecular structures that are subsequently capable of intermolecular association leading to formation of a gel network. Consequently, it is desirable that the polymer is capable of forming a gel by another method, for example dissolving a sufficient concentration in hot distilled or demineralised water and allowing it to cool to a temperature low enough to permit gel formation (eg, an ambient temperature of about 20xc2x0 C.). Other methods of gel formation include, for example, pH changes (eg, for the formation of cold set whey gels).
Polymers which are dependent on polyvalent cations for gelling (eg, alginate and gellan gum) can be employed to produce gel particles and used in hair treatment compositions, so long as they are stabilised against the surfactant (by employing e.g. a protective structure, such as amylose, around or within the gel). Alternatively, cross-linking agents can be used to stabilise proteins or polysaccharides against the disruptive effect of surfactants on gel structure.
Compositions embodying this invention may be made with viscosities in a wide range. At one extreme, the compositions may be freely mobile, self-levelling and pourable, although thicker than water. On the other hand, they may be made as viscous liquids which can be squeezed from a collapsible container, and yet which are too viscous to pour, except very slowly.
They are shear-thinning, which can be a useful property in hair treatment compositions such as shampoos and conditioners, because the user can perceive the product as thick and viscous, and yet find it easy to apply. An advantage of viscous shear gels is that they are good at retaining the shape which has been squeezed out, and so can be dispensed by methods other than simple pouring such as from flexible or deformable squeeze tubes.
If the compositions are heated to a temperature above the melting temperatures, the individual gel particles will melt and will not reform as separate particles on cooling quiescently, but this will not be a problem in ordinary use, because reversible gels generally have melting temperatures well above normal room temperatures (eg, 20xc2x0 C.). (Irreversible gels are temperature stable by definition and include whey gels.)
Viscosity of compositions embodying this invention can be measured using the same techniques as are used to measure viscosities of other thickened liquid compositions. One suitable apparatus is the Haake Rotoviscometer(trademark), another is the Carri-Med CSL 500(trademark) viscometer.
Many compositions of this invention will display a viscosity in a range from 0.1 Pa.s to 1000 Pa.s at a shear rate of 10 sec-1 measured at 20xc2x0 C.
Typically, the gel particles in the shear gel phase will have an average size (ie, maximum dimension) in the range of from 1 xcexcm to 1000 xcexcm, more preferably 5 xcexcm to 100 xcexcm and most preferably 10 to 80 xcexcm, although particles having sizes falling outside this range may also be present in the shear gel phase.
One route for the preparation of the sheared gel particles required for this invention, according to the process of the invention, starts with the provision of an aqueous solution of the polymer, at a temperature above the gel melting temperature (and probably also above its order to disorder transition temperature), mixing the solution with particles or droplets of one or more hair benefit agents, which are substantially insoluble in, or immiscible with, the aqueous solution, then cooling the solution to a temperature below the gel setting temperature, while applying shear to the composition. Generally, the solution will be subjected to shear while cooling from, for example, 10xc2x0 C. higher than the gel melt temperature to, for example, 10xc2x0 C. to 20xc2x0 C. lower than the gel formation temperature.
On a small scale, this preparation may be carried out using a beaker and a mechanical stirrer to provide vigorous stirring while the contents of the beaker are allowed to cool.
We prefer to carry out the preparation using a scraped surface heat exchanger. This may be equipped to operate under a partial vacuum to reduce the incorporation of air bubbles into the composition as gel formation takes place.
Another possibility for preparing gel particles is to employ a xe2x80x9cStirred Potxe2x80x9d where the solution is quench cooled in a jacketed shear device fitted with a thermometer.
Alternatively, the shear gel may be formed by providing cooling by means of passing the solution and additives through a plate heat exchanger. Plate heat exchangers are well known units marketed by companies such as Alfa Laval and APV. In this device, the solution is transformed into a shear gel as it passes through channels of the plate heat exchanger. Shear is transmitted to the solution due to the flow through the channels, rather than by a rotor as in methods described previously in this application. The production of shear gels using the plate heat exchanger may take place in re-circulation mode or in single pass mode. In re-circulation mode the solution is pumped from the base of a stirred batch vessel into the plate heat exchanger and then back into the stirred tank. This operation terminates when the temperature of the entire batch has reached the desired value, below the gelation point of the polymer solution. In single pass mode, the solution will reach the desired temperature upon exiting from the heat exchanger. The plate heat exchanger may be operated in co-current or countercurrent mode with respect to the flow direction of the cooling medium. Through installation of suitable diverters the exchanger may be operated in single pass or multipass configuration, depending on heat transfer performance required in the particular application.
Furthermore, the plate heat exchanger may be operated in series with an in-line dynamic mixing device, such as a Silverson or Dispax mixer. This device provides the ability to break down the shear gel particles formed in the stirred vessel, scraped surface heat exchanger or plate heat exchanger. Thus the in line dynamic mixer provides some control over gel particle size.
We have found that for many polymers gel formation is inhibited by the presence of surfactant (which is normally a component of hair treatment compositions), and yet gel particles which have already been formed remain stable if surfactant is added subsequently.
Therefore, if the final composition is to contain a surfactant, generally it will be desirable to form the gel particles by cooling an aqueous solution of the gel-forming polymer in the substantial absence of surfactant, and then add surfactant subsequently. An alternative approach is to incorporate surfactant into the aqueous composition before the step of cooling under shear, but this is not possible for all gel-forming polymers.
Thus, the process of the invention may involve a method of preparing a composition comprising a surfactant (such as in a personal wash or hair treatment composition) as set forth above which comprises forming a hot (eg, 40xc2x0 C. to 100xc2x0 C.), mobile aqueous solution of the polymer, mixing the solution with particles or droplets of one or more substances which are substantially insoluble in, or immiscible with, the aqueous solution, cooling the solution through its gel temperature, subjecting it to shear during or after cooling, and incorporating surfactant possibly before but preferably after cooling through the gel temperature.
A laboratory-scale scraped surface heat exchanger which we have used successfully is the ESCO Labor(trademark) mixer available from ESCO Labor, CH-4125, Reihen, Germany.
Scraped surface heat exchangers (A-units) homogenisers and temperature controlled pin-mixers (C-units) are used in the commercial production of margarine and other spreadable foodstuffs and such apparatus may be used to produce compositions of this invention on a larger scale. A discussion of such heat exchangers is given by Harrod in Journal of Food Process Engineering 9 (1986) pages 1-62. Suppliers of such apparatus include Armfield Ltd, Ringwood, Hampshire, England, Contherm Corporation which is a division of the Alfa-Laval Group, USA and APV Projects (Crepaco) Ltd, Crawley, West Sussex, England.
An alternative jacketed shear device that has been used successfully to make the shear gels of the invention is the stirred pot (illustrated in FIG. 1b) which is cooled using a Tricool chiller system supplied by Tricool Engineering Limited, Solent House, 14 Barnes Wallis Road, Segensworth East, Fareham, Hampshire, PO5 5TT.
After the formation of gel particles, the addition of surfactant or other ingredients, probably as a liquid concentrate, can be carried out using conventional mixing apparatus, operating at low shear. A mixing operation should not be allowed to heat the composition sufficiently to cause the melting of the gel particles. If necessary, a composition containing gel particles should be cooled before and/or during any subsequent mixing operation.
One route for producing a protein shear gel is illustrated, for example, by the process of cold set whey gelation. Cold set gels are produced by a two step process, the first involves heating the protein under conditions where it does not gel but produces soluble nm size linear protein aggregates. This usually means at high or low pH and in the absence of salt. The aggregates are prevented from aggregating by electrostatic repulsion. These aggregates are then induced to gel by changing the solution conditions to remove this repulsion. This is either achieved by adding salt to screen the charge or changing the pH.
In order to produce a whey shear gel, this two step process is also carried out but the second gelation step is carried out under shear. This shear could be produced in a variety of methods as described earlier for example a xe2x80x98stirred potxe2x80x99 or a scraped surface heat exchanger. In order to entrap an ingredient within the whey particles, it may be added to the whey solution before the initial heating step, or after the heating step and before the gelation under shear. This addition is achieved by mixing the solution with particles or droplets of one or more substances which are substantially insoluble in, or immiscible with, the aqueous solution. The gelation is induced usually by a change in pH, for example, to take the solution from pH 7 to between pH 3.5 and 6. Preferably, this change can be achieved, by adding acid directly to the whey while it is under shear, or by adding a slow acidifier for example GDL (glucono-xcex4-lactone) which will change the pH slowly while the sample is sheared.